Wavemeter having strip-line resonator capacitively coupled to feed, with movable dielectric effectively varying resonator length



06b1, 1963 K. FOSTER ETAL 3 ,9 7

WAVEMETER HAVING STRIP-LINE RESONATOR CAPACITIVELY COUPLED TO FEED, WITH MOVABLE DIELECTRIC EFFECTIVELY VARYING RESONATOR LENGTH Filed March 11, 1960 I2 74 ll 1 FgS.

A T TORNE Y United States Patent 3,105,947 WAVEMETER HAVING STRIP-LINE RESONATOR CAPACITIVELY COUPLED T0 FEED, WITH MOVABLE DIELECTRIC EFFECTIVELY VARY- ING RESONATOR LENGTH Kenneth Foster, Cockfosters, and John Horace Langley, Harlow, England, assignors to A. C. Cossor Limited, London, England, a British company Filed Mar. 11, 1960, Ser. No. 14,417 4 Claims. (Cl. 333-82) The present invention relates to wavemeters for use in strip-line transmission systems.

A strip-line transmission system comprises an elongated conductor arranged between and spaced and electrically insulated from two substantially flat conducting plates, known as earth planes, which are electrically connected together and usually connected to earth. Conviently the elongated conductor is supported upon an insulating sheet which may extend on either Side of the conductor and -be clamped between the earth planes through suitable spacers. There may be two conductors in register with one another on the two sides of the insulating sheet. The conductors may be in the form of metal foil or may be applied for example by a printed circuit technique.

According to the present invention there is provided a strip-line wavemeter comprising an elongated conductor mounted between and spaced and electrically insulated from two fiat conducting earth planes which are electrically connected together, a further conductor spaced from, and extending laterally away from the elongated conductor, and means for varying the capacitance between the further conductor and the earth planes.

The invention will be described, by way of example, with reference to the accompanying drawing in which FIG. 1 is a plan view, .partly broken away, of one embodiment of the invention,

FIG. 2 is a view in section on the line 22 of FIG. 1, and

FIG. 3 is a plan view of a part of a modified embodiment of the invention.

Referring to FIGS. 1 and 2, a strip-line transmission system comprises two earth planes and 11 having clamped between them as insulating sheet 12 of low loss material. Spacers '13 are provided to maintain the sheet 12 spaced suitably from the earth planes and the assembly is clamped together by bolts 14.

On each side of the sheet 12 is a conducting strip 15. Only one of the strips is shown but they are in register with one another. End connectors 16 and 17 are provided for coupling the strip-line device between coaxial cables (not shown). In this example the sheet 12 is a laminate formed of layers of silicon glass cloth bonded with silicone resin. The conductors 15 are strips of copper foil bonded to the sheet 12 by means of an epoxy resin. The two conductors 15 are connected together at their two ends where they join the connectors 16 and 17 and may also be connected together at one or more points intermediate the ends, for instance by means of rivets.

A member 18 is fixed to one edge of the earth planes 10 and 11 and serves as a support for two guide pins 19. A T-shaped member is slidably mounted on the guide pins 19 which pass through holes in the cross-piece of "ice the T. Movements of the member 20 in the directions of the arrows 21 is effected by a micrometer screw 22 threaded into the member 18 and operated by an extension 23. The screw 22 is coupled to the member 20 in any convenient manner permitting relative rotation but preventing relative movements in the directions 21. To the stem of the T are fixed two plates 24 of material of high dielectric constant so spaced apart as to allow the edge of the sheet 12 to slide freely between them. An example of a suitable material for the plates 24 is polystyrene loaded with titanate. Two further conducting strips 25 are fixed in register with one another on opposite sides of the sheet '12, and extend at right angles from the conductors 15, the strips 25 being spaced from the conductors 15 but being sufficiently close to the conductors 15 to be electrically coupled thereto. The arrangement in such that the plates 24 can be made to overlap the stripes 25 to a greater or less extent as the plates 24 are moved by means of the micrometer 22, 23. In this way the capacitive coupling between the strips 25 andthe earth planes can be varied.

In order to measure the frequency of radio waves propagating through the strip-line system 10, 11, 15, a measuring instrument indicating the amount of radio frequency energy passing through the strip-line system is connected thereto. The instrument may, under suitable conditions, be a crystal detector followed by an ammeter. The micrometer 22, 23 is adjusted until the indication on the instrument is a minimum, thereby indicating maximum absorption of energy by the capacitively coupled conductors 25. The micrometer 22, 23 may be calibrated in frequency or wavelength.

If desired the conductors 25 or plates 24 may be of other than rectangular shape and such that the relation between change in capacitance and movement of the plates 24 departs from a linear relation in a desired manner. A like effect can be produced by making the plates 24 of non-uniform thickness.

In the modification shown in FIG. 3, the insulating sheet 12 is provided with a slot 26 into which slides an extension 22 of the micrometer screw 22 of FIGS. 1 and 2. The conductors 25 of FIGS. ,1 and 2 are replaced by a U-shaped conducting coating 25', the inside edges of the limbs of the U being set back so as to be out of electrical contact with the electrically conducting extension 22. This modification operates in the same way as the embodiment of FIGS. 1 and 2.

The device described is of particular use in radar systems, although it may find application in any radio system.

We claim:

1. A strip-line wavemeter comprising two electrically connected fiat conducting earth planes disposed parallel to one another and spaced apart, a sheet of insulating material, an elongated conductor carried upon each side of said sheet of insulating material, means insulatingly supporting said sheet between said earth planes with said conductors air-spaced from said earth planes, a further pair of conductors spaced from, electrically coupled to and extending laterally away from said elongated conductors, and means for varying the capacitance between said further pair of conductors and said earth planes, comprising a moveable member in overlapping relation to said further pair of conductors and being slidable between a position of substantially no overlap with said further conductors and a position of substantially complete overlap with said further conductors.

2. A strip-line wavemeter according to claim 1 wherein said sheet of insulating material is slotted and wherein said movable member is movable into and out of said 5 slot.

3. A strip-line Wavemeter according to claim 2, wherein the further conductors are of approximately U shape and extend around the slot.

4-. A strip-line waverneter according to claim 1 Wherein said eaipacitancevaryin-g moveable member comprises two plates of dielectric material each slidable between one of said further conductors and one of said earth planes.

References Ciied in the file of this patent UNITED STATES PATENTS 2,760,169 Engelmann Aug. 21, 1956 r 2,909,736 Somrners et al. Oct. 20, 1959 2,964,718 Packard Dec. 13, 1960 FOREIGN PATENTS 767,067 Great Britain Jan. 30, 1957 OTHER REFERENCES Michelson: Resonator and Preselector in Balanced Strip Line, IRE Transactions on Microwave Theory and Techniques, vol. MTT3, No. 2, March 1955, pp. 170-174. 

1. A STRIP-LINE WAVEMETER COMPRISING TWO ELECTRICALLY CONNECTED FLAT CONDUCTING EARTH PLANES DISPOSED PARALLEL TO ONE ANOTHER AND SPACED APART, A SHEET OF INSULATING MATERIAL, AN ELONGATED CONDUCTOR CARRIED UPON EACH SIDE OF SAID SHEET OF INSULATING MATERIAL, MEANS INSULATINGLY SUPPORTING SAID SHEET BETWEEN SAID EARTH PLANES WITH SAID CONDUCTORS AIR-SPACED FROM SAID EARTH PLANES, A FURTHER PAIR OF CONDUCTORS SPACED FROM, ELECTRICALLY COUPLED TO AND EXTENDING LATERALLY AWAY FROM SAID ELEONGATED CONDUCTORS, AND MEANS FOR VARYING THE CAPACITANCE BETWEEN SAID FURTHER PAIR OF CONDUCTORS AND SAID EARTH PLANES, COMPRISING A MOVEABLE MEMBER IN OVERLAPPING RELATION TO SAID FURTHER PAIR OF CONDUCTORS AND BEING SLIDABLE BETWEEN A POSITION OF SUBSTANTIALLY NO OVERLAP WITH SAID 